This Night Optics 38mm Clip-On Rail Mount is designed to be used with the company's Krystal 950 and D-930 clip-on night vision riflescopes. Made of anodized aluminum, it mounts on your gun's Picatinny rail and has a base height of 38mm, assuring correct alignment with day optics of the same base height. It provides a solid connection between optic and weapon with no shift of zero.